Use this forum if you have installed hMailServer and want to ask a question related to a production release of hMailServer. Before posting, please read the troubleshooting guide. A large part of all reported issues are already described in detail here.

I see on this forum some people who set this value max number of command threads to 500
Why can't I set more than 10 ?
Performance should be better with a greater value for the max number of threads.
How can I configure my server for the best performance ?

If indexing is turned off, webmail clients with large sorted mailboxes will overload your server.

If you turn it on, message indexing will overload hMailServer 5.3.0 + MS SQL Compact Ed. Get better SQL server. If you have database separated from hMailServer, your setup might be able to use more than one core or cpu. Or I made mistake about your setup and SQL Express is not same thing that you get in default hMailServer package.